1. Technical Field
The present invention relates to an inkjet image forming apparatus, and particularly, to an inkjet image forming apparatus employing an ink circulation system that circulates an ink through a print head.
2. Background Arts
There are inkjet printers capable of high-speed color printing, costing low. They are remarkably widespread. Most types of inkjet printers are connectable to a terminal, such as a personal computer, to take in image data, such as letters, illustrations and marks, produced at the terminal, and print the image data on a sheet. Composite types of inkjet printers have an integrated scanner or facsimile to take in image data through the scanner and print them; or to receive image data transferred to the facsimile and print them.
Some types of inkjet printers are likely to use a high-viscous ink to prevent sheets from being stained with ink. This is to enhance the quality of print image. Using such an ink permits the print image quality to be enhanced. However, high-viscous inks tend to stagnate in a flow passage. Some types of ink might be unlikely to flow in inkjet printers employing an ink supply system in which the ink used runs down by own weight, as discussed in the Japanese Patent Application Laid-Open Publication No. 2004-188857. Using such an ink might constitute a difficulty for ink supply to be smooth all the way from an ink storage section to a print head, as an issue.
The Patent Literature has disclosed an inkjet printer including an intermediate ink storage portion between the ink storage section and the print head. The intermediate ink storage portion has a pressure retaining mechanism to retain pressures acting on a liquid level of stored ink within an atmospheric pressure range. This inkjet printer is adapted to supply ink from the intermediate ink storage portion to the print head with an even pressure, as a solution to the issue above.
On the other hand, inkjet printers are given a prescribed temperature range. This is to ensure the performance that a type of ink used for the printing should have to attain a favorable printing result. There are inkjet printers employing an ink circulation system to be effective to ensure the performance of ink. This system always circulates an ink, unlike the system in which an ink runs down by own weight. In that system, the ink being circulated can be controlled within a prescribed temperature range.
Such inkjet printers include a print head, an ink storage tank, and an ink circulation line provided with a heater for heating ink flowing in the ink circulation line, and a cooler for cooling ink flowing in the ink circulation line. The ink circulation line has an ink supply line for supplying a flux of ink from the ink storage tank to the print head, and an ink return line for returning fluxes of ink collected from the print head to the tank. The ink temperature may become too low, deviating from a temperature range ensuring a performance of ink. In such situations, the heater is operated to heat the ink. Also, the ink temperature may become too high, deviating from the temperature range ensuring the performance of ink. In such situations, the cooler is operated to cool the ink. Inkjet printers employing such an ink circulation system are adapted to use a combination of a heater and a cooler to control an ink temperature. It therefore is possible to make use of a performance of ink to a maximum degree, with a favorable printing result allowing for an enhanced print image quality.